1. Field of the Invention
The present invention relates to a tamper resistant apparatus for a CATV system which apparatus is connected between a trunk and an interdiction system or other program denial means such as negative traps which are located at a subscriber's home, whereby attempts to tamper with transmission of premium programs (in the clear) to the program denial means on the subscriber's home are detected and program denial is effected.
2. Background Description
FIG. 1 illustrates the problem with conventional interdiction systems or other program denial means, wherein signals are sent unscrambled (in the clear) along a trunk or feeder cable 10 to a pole mounted tap 12, down a drop cable 14 until they reach the program denial means 16, which may be located on the side of a home 18 for convenience and ease of access for the cable installer. The program denial means 16 is powered by cable 20 and grounded by cable 22 and supplies a scrambled signal along cable 24 to a subscriber's dwelling. However, when this is done, the signals come to the home 18 before being scrambled, resulting in additional opportunities for the subscriber to steal signals. For example, should the subscriber install a tap (available at popular electronics stores and home centers) before the program denial means 16, he or she will receive all signals regardless of whether he or she has purchased them.
In a simple situation such as the illustration of FIG. 1, the installation could be audited periodically to ascertain that the subscriber has not tapped in ahead of the interdiction device. However, in the more general cases, plants may be growing over the drop cable, rendering visual inspection difficult. In many areas today, the cable would be installed underground, rendering auditing impossible.
In order to accommodate a reasonable degree of security in such situations, it is desirable to have available some sort of security which will detect intervention by an unauthorized person, and will deny any signals under such conditions.
One system for detecting tampering in a CATV system is disclosed in U.S. Pat. No. 4,443,815. In this system a wired program distribution tamper detection circuit useful in CATV is connected in the subscriber drop cable between the trunk and a subscriber's TV set and cuts off the program signal in the event the cable is momentarily disconnected as would occur during tampering. The circuit detects an abnormal impedance, in its general form, or the interruption of a DC path through the cable, in its preferred embodiment, and inhibits the application of the signal upon such detection. A complaint by the subscriber thus effects an announcement of the tampering. Subsequently, a serviceman must be sent to the subscriber's home, and is able to reestablish service by the mere push of a button which is hidden within the connector housing.
In the tamper detection circuit disclosed in the above patent, a serviceman is required to be sent to a subscriber's home which can be costly and inconvenient. In addition, the tamper resistant circuit is not addressable from the headend.